Systems and methods for haptic control of a surgical tool

ABSTRACT

A surgical system includes a surgical tool and a processing circuit. The processing circuit is configured to provide a plurality of virtual haptic interaction points where each virtual haptic interaction point is associated with a portion of the surgical tool such that movement of the surgical tool corresponds to movement of the plurality of virtual haptic interaction points, establish a haptic object that defines a working boundary for the surgical tool, and constrain at least one of the portions of the surgical tool based on a relationship between at least one of the plurality of virtual haptic interaction points and the haptic object.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/824,867, filed Aug. 12, 2015, which is a continuation of U.S.application Ser. No. 13/725,348, filed Dec. 21, 2012, each of which isincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates generally to the field of haptics, andmore particularly to haptic control of a surgical tool.

During computer-assisted surgeries, a surgeon may utilize a hapticdevice. “Haptic” refers to a sense of touch, and the field of hapticsrelates to, among other things, human interactive devices that providefeedback to an operator. Feedback may include tactile sensations suchas, for example, vibration. Feedback may also include providing force toa user, such as a positive force or a resistance to movement. A commonuse of haptics is to provide a user of the device with guidance orlimits for manipulation of that device. For example, a haptic device maybe coupled to a surgical tool, which can be manipulated by a surgeon toperform a surgical procedure. The surgeon's manipulation of the surgicaltool can be guided or limited through the use of haptics to providefeedback to the surgeon during manipulation of the surgical tool.

A surgical plan is typically developed prior to performing a surgicalprocedure with a haptic device. The surgical plan may bepatient-specific. Based on the surgical plan, the surgical system guidesor limits movements of the surgical tool during portions of the surgicalprocedure. Control of the surgical tool serves to protect the patientand to assist the surgeon during implementation of the surgical plan.

In general, haptic devices for use during surgical procedures can haveat least two modes of operation. In free mode, the surgeon cansubstantially freely manipulate the surgical tool coupled to the device.In haptic control mode, components of the surgical system (e.g., hapticobjects) are activated to guide or limit movements of the surgical tool.Use of prior art haptic devices may be enhanced by a mechanism toimprove transitions between free mode and haptic control mode during asurgical procedure.

SUMMARY

One embodiment relates to a surgical system. The surgical systemincludes a surgical tool and a processing circuit. The processingcircuit is configured to provide a plurality of virtual hapticinteraction points where each virtual haptic interaction point isassociated with a portion of the surgical tool such that movement of thesurgical tool corresponds to movement of the plurality of virtual hapticinteraction points, establish a haptic object that defines a workingboundary for the surgical tool, and constrain at least one of theportions of the surgical tool based on a relationship between at leastone of the plurality of virtual haptic interaction points and the hapticobject.

Another embodiment relates to a method for using a surgical system. Themethod includes providing a surgical tool; providing a plurality ofvirtual haptic interaction points associated with a plurality ofportions of the surgical tool such that movement of the surgical toolcorresponds to movement of the plurality of virtual haptic interactionpoints; establishing a haptic object that defines a working boundary forthe surgical tool; and constraining at least one of the portions of thesurgical tool based on a relationship between at least one of theplurality of virtual haptic interaction points and the haptic object.

A still further embodiment relates to a computer-readable storage mediumhaving instructions thereon that, when executed by a processing circuit,aid in the planning or performance of a surgical procedure. The mediumincludes instructions for associating a plurality of portions of asurgical tool with a plurality of virtual haptic interaction points suchthat movement of the surgical tool corresponds to movement of theplurality of virtual haptic interaction points, instructions foractivating a haptic object that defines a working boundary for thesurgical tool, and instructions for constraining at least one of theplurality of portions of the surgical tool within the working boundarybased on a relationship between at least one of the plurality of virtualhaptic interaction points and the haptic object.

Alternative exemplary embodiments relate to other features andcombinations of features as may be generally recited in the claims.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure will become more fully understood from the followingdetailed description, taken in conjunction with the accompanyingfigures, wherein like reference numerals refer to like elements, inwhich:

FIG. 1 is a surgical system according to an exemplary embodiment.

FIGS. 2A and 2B are embodiments of a sagittal saw.

FIGS. 3A and 3B illustrate planned femur modifications according to anexemplary embodiment, and FIGS. 3C and 3D illustrate planned tibiamodifications according to an exemplary embodiment.

FIG. 4 illustrates a method for using a surgical system, according to anexemplary embodiment.

FIGS. 5A-5E illustrate entry and exit from haptic control when the toolnormal is perpendicular to the haptic object, according to an exemplaryembodiment.

FIGS. 6A and 6B show the haptic object of FIGS. 5A-5E, according to anexemplary embodiment.

FIGS. 7A and 7B illustrate an offset haptic object according to anexemplary embodiment.

FIGS. 8A-8E illustrate entry and exit from haptic control when the toolaxis is perpendicular to the haptic object, according to an exemplaryembodiment.

FIGS. 9A and 9B show the haptic object of FIGS. 8A-8E, according to anexemplary embodiment.

FIG. 10 illustrates another embodiment of an offset haptic object,according to an exemplary embodiment.

FIGS. 11A-11E illustrate entry and exit from haptic control when thehaptic object is a line, according to an exemplary embodiment.

FIG. 12 illustrates various features of the surgical plan of theembodiment of FIGS. 11A-11E.

FIGS. 13A-13D illustrate entry and exit from haptic control when thehaptic object is a three-dimensional volume, according to an exemplaryembodiment.

FIG. 14 illustrates various features of the surgical plan of theembodiment of FIGS. 13A-13D.

FIG. 15 illustrates a haptic restoration feature employed when hapticcontrol is disengaged.

FIG. 16 illustrates an entry boundary, according to an exemplaryembodiment.

DETAILED DESCRIPTION

Before turning to the figures, which illustrate the exemplaryembodiments in detail, it should be understood that the application isnot limited to the details or methodology set forth in the descriptionor illustrated in the figures. It should also be understood that theterminology is for the purpose of description only and should not beregarded as limiting. For example, several illustrations depict methodsrelated to haptic control entry and exit when performing specificsurgical procedures on a patient's knee. However, the embodiments ofhaptic control described herein may be applied to haptic control of asurgical tool during any type of surgical procedure on any part of apatient, including a patient's shoulder, arm, elbow, hands, hips, legs,feet, neck, face, etc.

Exemplary Surgical System

Referring to FIG. 1, a surgical system 100 includes a navigation system10, a computer 20, and a haptic device 30. The navigation system tracksthe patient's bone, as well as surgical tools utilized during thesurgery, to allow the surgeon to visualize the bone and tools on adisplay 24 and to enable haptic control of a surgical tool 36 coupled tothe haptic device 30.

The navigation system 10 may be any type of navigation system configuredto track a patient's anatomy and surgical tools during a surgicalprocedure. For example, the navigation system 10 may include anon-mechanical tracking system, a mechanical tracking system, or anycombination of non-mechanical and mechanical tracking systems. Thenavigation system 10 obtains a position and orientation (i.e. pose) ofan object with respect to a coordinate frame of reference. As the objectmoves in the coordinate frame of reference, the navigation system tracksthe pose of the object to detect movement of the object.

In one embodiment, the navigation system 10 includes a non-mechanicaltracking system as shown in FIG. 1. The non-mechanical tracking systemis an optical tracking system with a detection device 12 and a trackableelement (e.g. navigation marker 14) that is disposed on a tracked objectand is detectable by the detection device 12. In one embodiment, thedetection device 12 includes a visible light-based detector, such as aMicronTracker (Claron Technology Inc., Toronto, CN), that detects apattern (e.g., a checkerboard pattern) on a trackable element. Inanother embodiment, the detection device 12 includes a stereo camerapair sensitive to infrared radiation and positionable in an operatingroom where the surgical procedure will be performed. The trackableelement is affixed to the tracked object in a secure and stable mannerand includes an array of markers having a known geometric relationshipto the tracked object. As is known, the trackable elements may be active(e.g., light emitting diodes or LEDs) or passive (e.g., reflectivespheres, a checkerboard pattern, etc.) and have a unique geometry (e.g.,a unique geometric arrangement of the markers) or, in the case ofactive, wired markers, a unique firing pattern.

In operation, the detection device 12 detects positions of the trackableelements, and the surgical system 100 (e.g., the detection device 12using embedded electronics) calculates a pose of the tracked objectbased on the trackable elements' positions, unique geometry, and knowngeometric relationship to the tracked object. The navigation system 10includes a trackable element for each object the user desires to track,such as the navigation marker 14 located on the tibia 2, navigationmarker 16 located on the femur 4, haptic device marker 18 (to track aglobal or gross position of the haptic device 30), and an end effectormarker 19 (to track a distal end of the haptic device 30).

Referring again to FIG. 1, the surgical system 100 further includes aprocessing circuit, represented in the figures as a computer 20. Theprocessing circuit includes a processor and memory device. The processorcan be implemented as a general purpose processor, an applicationspecific integrated circuit (ASIC), one or more field programmable gatearrays (FPGAs), a group of processing components, or other suitableelectronic processing components. The memory device (e.g., memory,memory unit, storage device, etc.) is one or more devices (e.g., RAM,ROM, Flash memory, hard disk storage, etc.) for storing data and/orcomputer code for completing or facilitating the various processes andfunctions described in the present application. The memory device may beor include volatile memory or non-volatile memory. The memory device mayinclude database components, object code components, script components,or any other type of information structure for supporting the variousactivities and information structures described in the presentapplication. According to an exemplary embodiment, the memory device iscommunicably connected to the processor via the processing circuit andincludes computer code for executing (e.g., by the processing circuitand/or processor) one or more processes described herein.

The computer 20 is configured to communicate with the navigation system10 and the haptic device 30. Furthermore, the computer 20 may receiveinformation related to surgical procedures and perform various functionsrelated to performance of surgical procedures. For example, the computer20 may have software as necessary to perform functions related to imageanalysis, surgical planning, registration, navigation, image guidance,and haptic guidance.

The haptic device 30 includes a base 32, a robotic arm 34, and asurgical tool 36 coupled to the robotic arm 34. The surgical tool may beany surgical tool that can be coupled to the robotic arm 34. Forexample, in the embodiment of FIG. 1, the surgical tool 36 is aspherical burr. The surgical tool 36 may also be a sagittal saw 38,shown in FIG. 2A, or sagittal saw 40, shown in FIG. 2B. The blade 39 ofsagittal saw 38 is aligned parallel to tool axis 42, while the blade 39of sagittal saw 40 is aligned perpendicular to tool axis 42. The surgeoncan choose between a spherical burr, sagittal saw 38, sagittal saw 40,or any other type of surgical tool depending on the type of bonemodification (e.g. hole, planar cut, curved edge, etc.) the surgeondesires to make.

A surgeon interacts with haptic device 30 to perform surgical procedureson a patient. In general, haptic device 30 has two modes of operation.In free mode, the surgeon can substantially freely manipulate the poseof the surgical tool 36. In haptic control mode, one or more hapticobjects 52 are activated. The haptic object 52 can constrain thesurgical tool 36 as described in various embodiments herein.

Development of a Surgical Plan

A surgical plan is created prior to a surgeon's performance of asurgical procedure. The surgical plan is developed utilizing athree-dimensional representation of a patient's anatomy, also referredto herein as a virtual bone model 45 (see FIGS. 3A-3D). A “virtual bonemodel” may include virtual representations of cartilage or other tissuein addition to bone. To obtain the virtual bone model 45, the computer20 receives images of the patient's anatomy on which the surgicalprocedure is to be performed. The patient's anatomy may be scanned usingany known imaging technique, such as CT, Mill, or ultrasound. The scandata is then segmented to obtain the virtual bone model 45. For example,prior to a surgical procedure on the knee, a three-dimensionalrepresentation of the femur 4 and tibia 2 is created. Alternatively, thevirtual bone model 45 may be obtained by selecting a three-dimensionalmodel from a database or library of bone models. In one embodiment, theuser may use input device 22 to select an appropriate model. In anotherembodiment, the computer 20 may be programmed to select an appropriatemodel based on images or other information provided about the patient.The selected bone model(s) from the database can then be deformed basedon specific patient characteristics, creating a virtual bone model 45for use in surgical planning and implementation as described herein.

The surgeon can create a surgical plan based on the virtual bone model45. The surgical plan may include the desired cuts, holes, or othermodifications to a patient's bone 44 to be made by the surgeon using thesurgical system 100. The modifications may be planned based on theconfiguration of a component to be coupled to the bone during thesurgery. For example, prior to performance of total knee arthroplasty,the surgical plan may include the planned modifications to boneillustrated in FIGS. 3A-3D. FIGS. 3A and 3B illustrate a virtual bonemodel 45 of a femur 4 that includes planned modifications to the femur4, including anterior cut 46, anterior chamfer cut 92, distal cut 84,posterior chamfer cut 94, and posterior cut 96. FIGS. 3C and 3Dillustrate a virtual bone model 45 of a tibia 2 that includes plannedmodifications to the tibia 2, including tibial floor cut 49, a wall cut51, and a peg cut 53. The planned modifications to the femur 4 shown inFIGS. 3A and 3B correspond to the virtual component 66 (FIG. 6A), whichrepresents a component to be coupled to the femur 4.

The surgical plan further includes one or more haptic objects that willassist the surgeon during implementation of the surgical plan byenabling constraint of the surgical tool 36 during the surgicalprocedure. A haptic object 52 may be formed in one, two, or threedimensions. For example, a haptic object can be a line (FIG. 11A), aplane (FIG. 6B), or a three-dimensional volume (FIG. 13A). Haptic object52 may be curved or have curved surfaces, and can be any shape. Hapticobject 52 can be created to represent a variety of desired outcomes formovement of the surgical tool 36 during the surgical procedure. Forexample, a haptic object 52 in the form of a line may represent atrajectory of the surgical tool 36. A planar haptic object 52 mayrepresent a modification, such as a cut, to be created on the surface ofa bone 44. One or more of the boundaries of a three-dimensional hapticobject may represent one or more modifications, such as cuts, to becreated on the surface of a bone 44. Furthermore, portions of athree-dimensional haptic object may correspond to portions of bone to beremoved during the surgical procedure.

Prior to performance of the surgical procedure, the patient's anatomy isregistered to the virtual bone model 45 of the patient's anatomy by anyknown registration technique. One possible registration technique ispoint-based registration, as described in U.S. Pat. No. 8,010,180,titled “Haptic Guidance System and Method,” granted Aug. 30, 2011, andhereby incorporated by reference herein in its entirety. Alternatively,registration may be accomplished by 2D/3D registration utilizing ahand-held radiographic imaging device, as described in U.S. applicationSer. No. 13/562,163, titled “Radiographic Imaging Device,” filed Jul.30, 2012, and hereby incorporated by reference herein in its entirety.Registration of the patient's anatomy allows for accurate navigation andhaptic control during the surgical procedure. When the patient's anatomymoves during the surgical procedure, the surgical system 100 moves thevirtual bone model 45 in correspondence. The virtual bone model 45therefore corresponds to, or is associated with, the patient's actual(i.e. physical) anatomy. Similarly, any haptic objects 52 created duringsurgical planning also move in correspondence with the patient'sanatomy, and the haptic objects 52 correspond to locations in actual(i.e. physical) space. These locations in physical space are referred toas working boundaries. For example, a linear haptic object 52corresponds to a linear working boundary in physical space, a planarhaptic object 52 corresponds to a planar working boundary in physicalspace, and a three-dimensional haptic object 52 corresponds to athree-dimensional volume in physical space.

The surgical system 100 further includes a virtual tool 47 (FIG. 5A),which is a virtual representation of the surgical tool 36. Tracking ofthe surgical tool 36 by the navigation system 10 during a surgicalprocedure allows the virtual tool 47 to move in correspondence with thesurgical tool 36. The virtual tool 47 includes one or more hapticinteraction points (HIPs), which represent and are associated withlocations on the physical surgical tool 36. As described further below,relationships between HIPs and haptic objects 52 enable the surgicalsystem 100 to constrain the surgical tool 36. In an embodiment in whichthe surgical tool 36 is a spherical burr, an HIP 60 may represent thecenter of the spherical burr (FIG. 11A). If the surgical tool 36 is anirregular shape, such as sagittal saws 38 or 40 (FIGS. 2A and 2B), thevirtual representation of the sagittal saw may include numerous HIPs.Using multiple HIPs to generate haptic forces (e.g. positive forcefeedback or resistance to movement) on a surgical tool is described inU.S. application Ser. No. 13/339,369, titled “System and Method forProviding Substantially Stable Haptics,” filed Dec. 28, 2011, and herebyincorporated herein in its entirety. In one embodiment of the presentinvention, a virtual tool 47 representing a sagittal saw includes elevenHIPs. As used herein, references to an “HIP” are deemed to also includereferences to “one or more HIPs.” For example, HIP 60 can represent oneor more HIPs, and any calculations or processes based on HIP 60 includecalculations or processes based on multiple HIPs.

During a surgical procedure, the surgical system 100 constrains thesurgical tool 36 based on relationships between HIPs and haptic objects52. In general, the term “constrain,” as used herein, is used todescribe a tendency to restrict movement. However, the form ofconstraint imposed on surgical tool 36 depends on the form of therelevant haptic object 52. A haptic object 52 may be formed in anydesirable shape or configuration. As noted above, three exemplaryembodiments include a line, plane, or three-dimensional volume. In oneembodiment, the surgical tool 36 is constrained because HIP 60 ofsurgical tool 36 is restricted to movement along a linear haptic object52. In another embodiment, the surgical tool 36 is constrained becauseplanar haptic object 52 substantially prevents movement of HIP 60outside of the plane and outside of the boundaries of planar hapticobject 52. The boundaries of the planar haptic object 52 act as a“fence” enclosing HIP 60. If the haptic object 52 is a three-dimensionalvolume, the surgical tool 36 may be constrained by substantiallypreventing movement of HIP 60 outside of the volume enclosed by thewalls of the three-dimensional haptic object 52. Because of therelationship between the virtual environment (including the virtual bonemodel 45 and the virtual tool 47) and the physical environment(including the patient's anatomy and the actual surgical tool 36),constraints imposed on HIP 60 result in corresponding constraints onsurgical tool 36.

Haptic Control During a Surgical Procedure

At the start of a surgical procedure, the haptic device 30 (coupled to asurgical tool 36) is typically in free mode. The surgeon is thereforeable to move the surgical tool 36 towards bone 44 in preparation forcreation of a planned modification, such as a cut or hole. Variousembodiments presented herein may facilitate the switch of haptic device30 from free mode to haptic control mode and from haptic control modeback to free mode, which may increase the efficiency and ease of use ofsurgical system 100.

One method for using a surgical system is illustrated in FIG. 4. In step401, a surgical tool is provided. A virtual HIP is also provided, whichis associated with the surgical tool (e.g., surgical tool 36 of FIG. 1)such that movement of the HIP corresponds to movement of the surgicaltool 36 (step 402). The surgical method further includes providing avirtual entry boundary and a virtual exit boundary (step 403). Asdescribed further below, entry and exit boundaries are virtualboundaries created during surgical planning, and interactions between anHIP and the entry and exit boundaries may facilitate switching hapticdevice 30 between free mode and haptic control mode during a surgicalprocedure. In other words, interactions between the HIP and entry andexit boundaries facilitate entry into and exit from haptic control. Instep 404, a haptic object is activated. The activated haptic object canconstrain the surgical tool after the haptic interaction point crossesthe virtual entry boundary. In step 405, the haptic object isdeactivated after the HIP crosses the virtual exit boundary. Because thehaptic object may be deactivated substantially simultaneously with theHIP crossing the virtual exit boundary, the term “after” can includedeactivation that occurs at substantially the same time as the HIPcrosses the virtual exit boundary.

FIGS. 5A-5E illustrate the virtual environment during an embodiment ofentry into and exit from haptic control. In this embodiment, the virtualbone model 45 represents a femur 4, and virtual tool 47 represents asurgical tool 36 in the form of sagittal saw 38 (e.g. as shown in FIG.2A). A sagittal saw 38 may be useful for creating a variety of cutsduring a total knee arthroplasty, such as cuts corresponding to plannedanterior cut 46, posterior cut 96, and tibial floor cut 49 (FIGS.3A-3D). In the embodiment illustrated in FIGS. 5A-5E, the plannedmodification is anterior cut 46, which corresponds to the anteriorsurface 68 of a virtual implant component 66 (FIG. 6A). FIG. 3B shows aperspective view of the planned anterior cut 46 on a virtual bone model45. The virtual environment depicted in FIG. 5A includes a planar hapticobject 52. Planar haptic object 52 may also be an offset haptic object78 (described below). Planar haptic object 52 may be any desired shape,such as the shape shown in FIG. 6B. FIG. 6B illustrates haptic object52, a blade of virtual tool 47, and a virtual implant component 66 allsuperimposed on each other to aid in understanding the relationshipbetween the various components of the surgical plan. In this embodiment,haptic object 52 represents a cut to be created on femur 4. Hapticobject 52 is therefore shown in FIGS. 6A and 6B aligned with anteriorsurface 68 of the virtual implant component 66. The blade of virtualtool 47 is shown during haptic control mode, when haptic object 52 isactivated and the blade is confined to the plane of haptic object 52.

Referring again to FIG. 5A, entry boundary 50 is a virtual boundarycreated during development of the surgical plan. Interactions betweenHIP 60 and the entry boundary 50 trigger the haptic device 30 to switchfrom free mode to “automatic alignment mode,” a stage of haptic controldescribed more fully below. The entry boundary 50 represents a workingboundary in the vicinity of the patient's anatomy, and is designed andpositioned such that the surgeon is able to accurately guide thesurgical tool 36 to the working boundary when the haptic device 30 is infree mode. The entry boundary 50 may, but does not necessarily, enclosea portion of a haptic object 52. For example, in FIG. 5A, entry boundary50 encloses a portion of haptic object 52.

FIG. 5A presents a cross-section of the virtual environment. In thisembodiment, entry boundary 50 is pill-shaped and encloses athree-dimensional volume. The pill-shaped entry boundary 50 has acylindrical portion with a radius R (shown in FIG. 7A) and twohemispherical ends also having radius R (not shown). A target line 54forms the cylinder axis (perpendicular to the page in FIG. 5A). Thetarget line 54 passes through a target point 55, which is the center ofentry boundary 50 in the illustrated cross section. Entry boundary 50can also be any other shape or configuration, such as a sphere, a cube,a plane, or a curved surface.

In one embodiment, entry boundary 50 can be a “Pacman-shaped” entryboundary 50 a, as shown in FIG. 16. The Pacman-shaped entry boundary isformed by cutting out a segment of a pill-shaped entry boundary, asdescribed above, to form an entry boundary 50 a having the cross sectionshown in FIG. 16. In this embodiment, the entry boundary 50 a istherefore a three-dimensional volume shaped as a pill with a removedsegment, such that a cross section of the virtual entry boundary issector-shaped (i.e., “Pacman-shaped”). Pacman-shaped entry boundary 50 aincludes two intersecting haptic walls 52 a. A target line 54(perpendicular to the page in FIG. 16) represents the intersection ofhaptic walls 52 a. Target point 55 is the center of target line 54.Haptic walls 52 a are an embodiment of the haptic objects 52 describedherein, and can therefore constrain movement of a surgical tool 36 bysubstantially preventing HIP 60 from crossing haptic walls 52 a. Hapticwalls 52 allow the Pacman-shaped entry boundary 50 a to create a safezone in front of the patient's bone. The Pacman-shaped entry boundary 50a can be used as the entry boundary in any of the embodiments describedherein to protect the patient's bone when a surgical tool is approachingthe patient. FIG. 16 illustrates virtual tool 47 (which corresponds tosurgical tool 36) as it makes contact with haptic wall 52 a. The hapticwall 52 a prevents the virtual tool 47 (and thus the surgical tool 36)from crossing haptic wall 52 a and approaching the patient's bone.

At the beginning of a surgical procedure, the surgeon guides surgicaltool 36 towards the working boundary represented by entry boundary 50.Once the surgeon causes HIP 60 of the surgical tool 36 to cross entryboundary 50, the surgical system 100 enters automatic alignment. Priorto or during automatic alignment, the surgical system 100 performscalculations to reposition and reorient surgical tool 36. In oneembodiment, the calculations include computing distance 58 (see FIG.5B). If the surgical tool 36 is a spherical burr, distance 58 mayrepresent the shortest distance line between a single HIP 60 and targetline 54 (e.g. as shown in FIG. 11B) or another reference object. Whenthe surgical tool 36 is a sagittal saw 38 or 40, the calculations toreposition and reorient surgical tool 36 may be based on the position ofmultiple HIPs relative to target line 54 or other reference object,although a distance 58 may still be calculated.

After performing the necessary calculations, the surgical system 100 isable to automatically align the surgical tool 36 from the pose ofvirtual tool 47 shown in FIG. 5B to the pose of virtual tool 47 shown inFIG. 5C. The haptic control embodiments described herein may (1)automatically modify the position of surgical tool 36 (i.e. reposition),(2) automatically modify the orientation of surgical tool 36 (i.e.reorient), or (3) both automatically reposition and reorient thesurgical tool 36. The phrase “automatic alignment” can refer to any ofscenarios (1), (2), or (3), and is a general term for modifying eitheror both of the position and orientation of the surgical tool 36. In theembodiment of FIGS. 5A-5E, for example, automatic alignment may alterboth the position and the orientation of surgical tool 36 relative to abone 44. Repositioning is accomplished by moving HIP 60 such that HIP 60lies within the plane of haptic object 52. In one embodiment, HIP 60 isrepositioned to lie on target line 54. Reorienting the surgical tool 36may be accomplished by rotating the virtual tool 47 such that thevirtual tool normal 48 is perpendicular to haptic object 52 (i.e. toolnormal 48 is parallel to the haptic object normal 62), as shown in FIG.5C. When the virtual tool 47 represents sagittal saw 38, aligning thevirtual tool normal 48 perpendicular to haptic object 52 causes theblade 39 of sagittal saw 38 to be accurately oriented relative to thebone 44. However, if the cutting portion of surgical tool 36 issymmetrical, such as when surgical tool 36 is a spherical burr, it maynot be necessary to reorient the surgical tool 36 during automaticalignment. Rather, surgical tool 36 might only be repositioned to bringHIP 60 within the plane of haptic object 52. After automatic alignmentis complete, surgical tool 36 is in place to perform a bone modificationaccording to the preoperative surgical plan.

The surgical system 100 may include a safety mechanism to provide thesurgeon with control during automatic alignment. The safety mechanismcan be designed to require certain actions (or continuation of anaction) by a user for completion of automatic alignment. In oneembodiment, the surgical system 100 produces an audible noise or otheralert when HIP 60 crosses entry boundary 50. The surgical system 100 isthen able to initiate automatic alignment. However, before an automaticalignment occurs, the surgeon must act by depressing a trigger orperforming another action. If the trigger is released during automaticalignment, the surgical system 100 may stop any automatic movement ofhaptic device 30 or cause haptic device 30 to enter free mode. Inanother embodiment, haptic device 30 includes a sensor to sense when thesurgeon's hand is present. If the surgeon removes his or her hand fromthe sensor during automatic alignment, the surgical system 100 may stopany automatic movement of haptic device 30 or cause haptic device 30 toenter free mode. The surgeon acts to ensure completion of automaticalignment by continuing to keep his or her hand on the sensor. Theseembodiments of a safety mechanism allow the surgeon to decide whetherand when to enable automatic alignment, and further allows the surgeonto stop automatic alignment if another object (e.g. tissue, aninstrument) is in the way of surgical tool 36 during automaticalignment.

Entry boundary 50 a of FIG. 16 is particularly beneficial if theabove-described safety mechanisms are being utilized. As oneillustration, the surgeon begins the haptic control processes describedherein by guiding surgical tool 36 towards the patient until thesurgical tool 36 penetrates an entry boundary. The surgical system 100then alerts the surgeon that the system is ready to begin automaticalignment. However, the surgeon may not immediately depress a trigger orperform some other action to enable the system to initiate the automaticalignment mode. During this delay, the surgical tool 36 remains in freemode, and the surgeon may continue to guide the tool towards thepatient. Accordingly, entry boundary 50 a shown in FIG. 16 includeshaptic walls 52 a. These walls 52 a prevent the surgeon from continuingto guide the surgical tool 36 (represented by virtual tool 47) towardsthe patient prior to enabling automatic alignment (e.g., via depressinga trigger or placing a hand on a sensor). The haptic walls 52 atherefore serve as a safety mechanism to protect the patient prior tothe surgical tool 36 being appropriately positioned and oriented toperform the planned bone modifications.

Referring to FIG. 5C, automatic alignment is complete and the pose ofsurgical tool 36 has been correctly modified, and the haptic device 30remains in haptic control mode. Haptic control mode, in general, can becharacterized by the activation of a haptic object 52 and the impositionof a constraint on the movement of a surgical tool 36 by the hapticobject 52. Automatic alignment can therefore be a form of haptic controlbecause haptic object 52 is activated, and surgical tool 36 isconstrained to specific movements to realign surgical tool 36 based onhaptic object 52. During the stage of haptic control shown in FIG. 5C,haptic object 52 is activated and HIP 60 is constrained within the planedefined by haptic object 52. The surgeon can therefore move surgicaltool 36 within the planar working boundary corresponding to hapticobject 52, but is constrained (e.g., prevented) from moving the surgicaltool 36 outside of the planar working boundary. The surgeon performs theplanned cut during haptic control mode. As the surgeon is cutting, thevirtual tool 47 can move in the x-direction from the positionillustrated in FIG. 5C to the position illustrated in FIG. 5D. Thevirtual tool 47 may also move back and forth in the z-direction incorrespondence with movement of surgical tool 36. However, planar hapticobject 52 restricts HIP 60 (and thus surgical tool 36) from movement inthe y-direction. FIG. 6B illustrates one embodiment of the shape ofhaptic object 52, shown with virtual tool 47 of FIG. 5C superimposed onhaptic object 52. A surgeon can reposition sagittal saw 38 within theworking boundary corresponding to haptic object 52, but the surgicalsystem 100 prevents sagittal saw 38 from crossing the outer bounds ofthe working boundary. FIG. 6A is a view of haptic object 52 aligned withanterior surface 68 of a virtual implant component 66. As mentionedpreviously, the modifications to bone, and thus the haptic objects 52,are typically planned to correspond to the configuration of a componentto be coupled to the bone during the surgical procedure.

During portions of haptic control mode, an exit boundary 64 is activated(see FIGS. 5C-5E). The exit boundary 64, like the entry boundary 50, isa virtual boundary created during development of the surgical plan.Interactions between HIP 60 and exit boundary 64 deactivate hapticobject 52 and trigger the haptic device 30 to switch from haptic controlmode back to free mode. The surgical system therefore remains in hapticcontrol mode and maintains surgical tool 36 within the working boundarycorresponding to haptic object 52 until HIP 60 crosses the exit boundary64. Once HIP 60 crosses the exit boundary 64 (e.g. by moving from theposition shown in FIG. 5D to the position shown in FIG. 5E) the hapticobject 52 deactivates and haptic device 30 switches from haptic controlmode to free mode. When haptic control is released, the surgical tool 36is no longer bound within the confines of a working boundary, but can bemanipulated freely by the surgeon.

In one embodiment, the exit boundary 64 is planar, located a distance Lfrom entry boundary 50 (see FIG. 7A), and has an exit normal 59. Duringhaptic control mode, the surgical system 100 continuously calculates thedistance from HIP 60 to exit boundary 64. Because exit normal 59 pointsaway from the patient's anatomy, the distance from HIP 60 to the exitboundary 64 will typically be negative during performance of bonemodifications (e.g. cutting, drilling). However, when the value of thisdistance becomes positive, haptic control is released by deactivation ofhaptic object 52, and the haptic device 30 enters free mode. In otherembodiments, the exit boundary 64 can be curved, three-dimensional, orany configuration or shape appropriate for interacting with HIP 60 todisengage haptic control during a surgical procedure. Simultaneously orshortly after the switch to free mode, exit boundary 64 is deactivatedand entry boundary 50 is reactivated. The surgeon can then reenterhaptic control mode by causing surgical tool 36 to approach the patientsuch that HIP 60 crosses entry boundary 50. Thus, the surgeon can moveback and forth between free mode and haptic control by manipulatingsurgical tool 36.

The entry boundary 50 and exit boundary 64 described in connection withthe various embodiments herein provide advantages over prior art methodsof haptic control. Some prior art embodiments employing haptic objectsrequire a separate action by a user to activate and deactivate hapticobjects and thus enter and exit haptic control. For example, to releasean HIP from the confines of a haptic object, the user might have topress a button or perform a similar action to deactivate the hapticobject. The action by the user deactivates the haptic object, which thenallows the surgeon to freely manipulate the surgical tool. Use of anexit boundary as described herein eliminates the need for the surgeon toperform a separate deactivation step. Rather, the surgeon must only pulla surgical tool 36 away from the patient to automatically deactivate ahaptic object 52 and exit haptic control. Embodiments of the presentdisclosure may therefore save time in the operating room. Furthermore,operation of a haptic device 30 may be more intuitive and user-friendlydue to the surgeon being able to switch conveniently between free modeand haptic control mode.

FIGS. 7A and 7B illustrate haptic object 52 and offset haptic object 78.A surgical plan may include an adjustable offset haptic object 78 totake into account characteristics of the surgical tool 36. Use of offsethaptic object 78 during haptic control mode of the haptic device 30 mayprovide additional accuracy during the surgical procedure by accountingfor the dimensions of the surgical tool 36. Thus, if the surgical tool36 is a spherical burr, the offset haptic object 78 may be translatedfrom haptic object 52 such that distance 80 (FIG. 7B) is equivalent tothe radius of the spherical burr. When offset haptic object 78 isactivated, the surgical system 100 constrains HIP 60 of the sphericalburr within the bounds of planar offset haptic object 78, rather thanconstraining the HIP 60 of the spherical burr within the bounds ofplanar haptic object 52. When constrained by the offset haptic object78, the edge of the spherical burr aligns with planned anterior cut 46.Similarly, if the surgical tool 36 is a sagittal saw 38, distance 80 maybe equivalent to half the thickness t of blade 39. FIG. 7B illustratesvirtual tool 47. In this embodiment, virtual tool 47 is the sagittal saw38 of FIG. 2A and includes a virtual blade 82. The virtual blade 82 hasa thickness t equivalent to the thickness of blade 39. When HIP 60 ofvirtual tool 47 is constrained to offset haptic object 78, the bottomedge of virtual blade 82 will align with planned anterior cut 46. Theactual cut created by the sagittal saw 38 during surgery will then moreclosely correspond to the planned anterior cut 46 than if HIP 60 wereconstrained to haptic object 52 of FIG. 7B.

In various embodiments, the surgical system 100 utilizes factors relatedto implementation of the surgical plan when calculating the parametersof adjustable offset haptic object 78. One factor may be the vibrationsof the surgical tool 36 during surgery, which can cause a discrepancybetween the actual dimensions of a surgical tool 36 and the effectivedimensions of the surgical tool 36. For example, a spherical burr with aradius of 3 mm may remove bone as though its radius were 4 mm. The burrtherefore has an effective radius of 4 mm. Similarly, due to vibrations,a blade 39 having a thickness of 2 mm may create a slot in bone having athickness of 2.5 mm. The blade 39 therefore has an effective thicknessof 2.5 mm. The offset haptic object 78 is created to take into accountthe effect of vibrations or other factors on surgical tool 36 toincrease the accuracy of the actual bone modification created duringsurgery.

The offset haptic object 78 may be adjustable. Adjustability isadvantageous because it allows a user to modify the offset haptic object78 without having to redesign the original haptic object 52. Thesurgical system 100 may be programmed to allow easy adjustment by theuser as new information is gathered prior to or during the surgicalprocedure. If the surgical plan includes offset haptic object 78,additional elements of the surgical plan may be similarly adjusted to anoffset position from their originally planned positions. For example,the surgical system 100 may be programmed to translate entry boundary 50and exit boundary 64 in the y-direction by the same distance as theoffset haptic object 78 is translated from the haptic object 52.Similarly, target line 54 and target point 55 may also be offset fromtheir initially planned position. It is to be understood that the“haptic object 52” referred to by many of the embodiments describedherein may technically be an “offset haptic object” with respect to theoriginal haptic object of the relevant surgical plan.

FIGS. 8A-8E illustrate the virtual environment during another embodimentof entry and exit from haptic control. In this embodiment, the virtualbone model 45 represents a femur 4. Virtual tool 47 represents asurgical tool 36 in the form of a sagittal saw 40 (e.g. as shown in FIG.2B). A sagittal saw 40 may be useful for performing a variety of cutsduring a total knee arthroplasty, such as cuts corresponding to planneddistal cut 84 and anterior chamfer cut 92. In the embodiment of FIGS.8A-8E, the planned modification is a planned distal cut 84, whichcorresponds to distal surface 72 of a virtual implant component 66 (FIG.9A). A perspective view of planned distal cut 84 is shown in FIG. 3B. Inthis embodiment, as in the embodiment of FIGS. 5A-5E, haptic object 52represents a cut to be created on femur 4. Haptic object 52 may be anyshape developed during surgical planning, such as the shape shown inFIG. 9B.

Referring again to FIGS. 8A-8E, entry into and exit into haptic controltakes place similarly as in the embodiment of FIGS. 5A-5E, differingprimarily in the automatic alignment and resulting orientation ofsurgical tool 36. Any applicable features disclosed in connection to theembodiment of FIGS. 5A-5E may also be present in the embodiment of FIG.8A-8E. In FIG. 8A, the haptic device 30 is in free mode and entryboundary 50 is activated. As the surgeon brings the surgical tool 36towards the patient's anatomy, the virtual tool 47 correspondinglyapproaches entry boundary 50. Once HIP 60 has crossed entry boundary 50,the surgical system 100 enters automatic alignment, during which thesurgical system 100 performs the necessary calculations and thenmodifies the position and orientation of surgical tool 36 (e.g. fromFIG. 8B to FIG. 8C). The position is modified to bring HIP 60 to thetarget line 54, and the orientation is modified to bring tool axis 42perpendicular to haptic object 52. Because the blade 39 of sagittal saw40 (FIG. 2B) is perpendicular to the tool axis 42, aligning the toolaxis 42 perpendicular to the haptic object 52 causes the blade to lie inthe x-y plane during the surgical procedure. Orientation of the toolaxis 42 in this embodiment contrasts to the embodiment of FIGS. 5A-5E,in which the tool axis 42 is oriented parallel to haptic object 52during cutting (e.g., FIG. 5C).

The surgical plan may be developed such that the surgical system 100will orient the surgical tool 36 in any desired direction relative tohaptic object 52. The desired orientation may depend on the type ofsurgical tool. For example, if the surgical tool 36 is a sagittal saw,the surgical system 100 may orient the surgical tool 36 differentlydepending on the type of sagittal saw (e.g. sagittal saw 38 or sagittalsaw 40) or the type of cut to be created. Furthermore, in someembodiments, the tool is repositioned but not reoriented duringautomatic alignment. For example, if the surgical tool 36 is a sphericalburr, the surgical system 100 may not need to modify the orientation ofthe surgical tool 36 to obtain the desired bone modification.

Once the surgical tool 36 has been automatically aligned as shown inFIG. 8C, HIP 60 is constrained within the plane defined by haptic object52. Entry into this stage of haptic control can trigger activation ofexit boundary 64. The surgeon performs the cut by manipulating thesurgical tool 36 within the planar working boundary corresponding tohaptic object 52 in the x-direction and the z-direction. FIGS. 8C and 8Dillustrate a change in position during cutting along the x-direction.When the surgeon moves the surgical tool 36 from the position shown inFIG. 8D to the position shown in FIG. 8E, HIP 60 crosses exit boundary64. The interaction between HIP 60 and exit boundary 64 deactivateshaptic object 52, releasing haptic control of surgical tool 36 andcausing haptic device 30 to once again enter free mode. Upon crossingthe exit boundary 64 or shortly thereafter, exit boundary 64 deactivatesand entry boundary 50 reactivates. The surgeon can then reenterautomatic alignment and haptic control during performance of bonemodifications by manipulating surgical tool 36 such that HIP 60 crossesentry boundary 50.

FIG. 10 illustrates haptic object 52 and offset haptic object 78 inrelation to planned distal cut 84. As described in connection with FIGS.7A and 7B, the adjustable offset haptic object 78 may be modifieddepending factors such as the dimensions of surgical tool 36 or otherfactors related to implementation of the surgical plan. The adjustmentof offset haptic object 78 can lead to adjustment of other plannedfeatures of the virtual environment, such as entry boundary 50, targetline 54, target point 55, and exit boundary 64.

The surgical plans depicted in FIGS. 7A-7B and 10 can be defined byvarious points and vectors. Normal origin point 57 lies on the originalhaptic object 52 and defines the origin of the haptic object normal 62as well as the exit normal 59. The haptic normal point 61 furtherdefines the haptic object normal 62, and may be located approximately 50mm from the normal origin point 57. The exit normal point 63 furtherdefines the exit normal 59, and may also be located approximately 50 mmfrom the normal origin point 57. Thus, the haptic object normal 62 canbe defined as the vector direction from the normal origin point 57 tothe haptic normal point 61, and the exit normal 59 can be defined as thevector direction from the normal origin point 57 to the exit normalpoint 63. The target point 55 may lie on the offset haptic object 78,and is offset from the normal origin point 57 in the direction of thehaptic object normal 62 by a desired amount. As explained above, thedesired amount may take into account the effective radius of a sphericalburr or half of the effective thickness of a sagittal saw blade 39. Thetarget line 54 can be defined by target point 55 and the cross productvector of exit normal 59 and haptic object normal 62, with endpoints onopposing edges of the offset haptic object 78.

FIGS. 11A-11E illustrate the virtual environment during anotherembodiment of entry and exit from haptic control. In this embodiment,the virtual bone model 45 represents a tibia 2. Virtual tool 47represents a surgical tool 36 in the form of a spherical burr, althoughthe surgical tool 36 can be any tool capable of creating planned hole88. The planned modification is a hole 88 to receive the peg of a tibialcomponent. The spherical burr can also be used to create holes forreceiving pegs of femoral, patellofemoral, or any other type of implantcomponent. In FIGS. 11A-11E, a virtual tibial component 90 issuperimposed on the bone model 45 to more clearly illustrate the plannedbone modifications. In this embodiment, haptic object 52 is a line. Theplacement of linear haptic object 52 may be planned based on thedimensions or effective dimensions of surgical tool 36, such as theradius TR of a spherical burr (FIG. 12). For example, a space equivalentto radius TR may be left between the end 95 of haptic object 52 and thebottom of peg tip point 91, as illustrated in FIG. 12.

FIG. 11A illustrates the virtual environment when haptic device 30 is infree mode. At the start of a surgical procedure, the surgeon movessurgical device 36 (FIG. 1) towards the patient until HIP 60 crossesentry boundary 50 (FIG. 11B). In this embodiment, entry boundary 50 is asphere having a radius R (FIG. 12) and having a target point 55 at itscenter. Once HIP 60 crosses entry boundary 50, the surgical systemautomatically aligns surgical tool 36. In one embodiment, the surgicalsystem 100 calculates the shortest distance from HIP 60 to target point55 and then repositions HIP 60 onto target point 55. The surgical system100 may also reorient surgical tool 36 such that tool axis 42 isparallel to haptic object 52 (FIG. 11C). HIP 60 is then constrained tomovement along linear haptic object 52, and the surgeon can movesurgical tool 36 along a linear working boundary corresponding to hapticdevice 52 to create hole 88 (FIG. 11D).

As in previous embodiments, the exit boundary 64 is activated duringportions of haptic control. When the surgeon desires to release hapticcontrol, the surgical tool 36 can be moved until HIP 60 crosses exitboundary 64 (FIG. 11E). Haptic object 52 is then deactivated, releasinghaptic control and causing the haptic device 30 to reenter free mode. Asdiscussed in relation to other embodiments, the surgical system 100 maycontinuously calculate the distance between HIP 60 and exit boundary 64,releasing haptic control when this distance becomes positive. Also asdescribed in connection with previous embodiments, entry boundary 50 canbe reactivated after release of haptic control. The surgeon can thenreenter haptic control by manipulating surgical tool 36 such that HIP 60crosses entry boundary 50.

FIG. 12 illustrates additional features of a surgical plan having alinear haptic object 52, such as the surgical plan of FIGS. 11A-11E. Thepeg axis is a line from peg tip point 91, located on the tip of plannedhole 88, to target point 55. Linear haptic object 52 may be a line onthe peg axis having a first endpoint at end 95 and a second endpointlocated past the target point 55 along the exit normal 59. For example,the second endpoint of haptic object 52 may located 50 mm past thetarget point 55 in the direction of exit normal 59. The exit boundary 64may be planar, located a distance L from the entry boundary 50, and havean exit normal 59 defined as the vector direction from the peg tip point91 to the target point 55.

FIGS. 13A-13D illustrate another embodiment of entry into and exit fromhaptic control. In this embodiment, haptic object 52 is athree-dimensional volume. Virtual bone model 45 can represent any bone44, such as a femur 4, and virtual tool 47 can represent any type ofsurgical tool 36 for performing any type of bone modifications. In thevirtual environment of FIG. 13A, haptic device 30 is in free mode. Toenter haptic control, the user manipulates surgical tool 36 towards thepatient's anatomy. Virtual tool 47, including HIP 60, move incorrespondence towards entry boundary 50. In this embodiment, entryboundary 50 is a plane that includes target point 55 (not shown). If HIP60 is within haptic object 52 and HIP 60 crosses entry boundary 50, asshown in FIG. 13B, haptic control is engaged. In haptic control mode,HIP 60 is prevented from exiting the confines of the three-dimensionalvolume defined by haptic object 52. Further, engagement of hapticcontrol triggers deactivation of entry boundary 50 and activation ofexit boundary 64 (FIG. 13C).

The embodiment of FIGS. 13A-13D does not include automatic alignment. Inother words, neither the position nor the orientation of surgical tool36 is modified during haptic control. Consequently, HIP 60 can be freelymoved to any position within haptic object 52, and the orientation ofsurgical tool 36 is not constrained by a haptic object. During hapticcontrol, the surgeon can freely move surgical tool 36 within the workingvolume corresponding to haptic object 52 to perform the necessary bonemodifications, such as cuts corresponding to planned distal cut 84,planned posterior chamfer cut 92, and planned posterior cut 96. FIG. 13Cillustrates virtual tool 47 as the surgeon is creating a cutcorresponding to planned posterior cut 96. During haptic control in theembodiment of FIGS. 13A-13D, as in previous embodiments, when HIP 60crosses exit boundary 64 (FIG. 13D), haptic control is released and thehaptic device 30 enters free mode. In alternative embodiments, thevirtual environment depicted in FIGS. 13A-13D includes additionalmechanisms to control the position of HIP 60. For example, planar hapticobjects along planned cuts 84, 94, and 96 could constrain HIP 60 tomovement along these planar haptic objects. The virtual environmentmight also include mechanisms to control the orientation of virtual tool47 (and therefore, of surgical tool 36), such as additional planar orlinear haptic objects on which HIP 60 can be constrained.

FIG. 14 illustrates the surgical plan of FIGS. 13A-13D. Exit boundary 64is parallel to entry boundary 50 and is located a distance L from entryboundary 50 in the direction of exit normal 59. Exit normal 59 is thevector direction from target point 55 to exit normal point 63. FIG. 14further includes a prior art haptic object 98. In a prior art method ofhaptic control, a user could not cause an HIP to exit haptic object 98without performing a separate action to disengage haptic control, suchas a pressing a button on input device 22 (FIG. 1). In contrast to priorart haptic object 98, the volumetric haptic object 52 extends fartherfrom the planned cutting surface. Further, the surgical plan associatedwith haptic object 52 includes an entry boundary 50 and an exit boundary64. In the presently disclosed embodiments, when the surgeon pullssurgical tool 36 away from the patient and causes HIP 60 to cross exitboundary 64, the surgical system 100 automatically deactivates hapticobject 52 to release haptic control. The provision of an exit boundary64 therefore allows the surgeon greater freedom to release hapticcontrol during surgery. In addition, the interaction between activationand deactivation of the entry boundary 50 and exit boundary 64 describedherein allows the surgeon to seamlessly and intuitively enter and exithaptic control by manipulating surgical tool 36, without having toperform separate actions to trigger entry into and exit from hapticcontrol.

FIG. 15 illustrates a haptic restoration feature that may be employed inany of the haptic control embodiments described herein. The hapticrestoration feature is applicable when haptic control is disengaged fora reason other than because HIP 60 has crossed the exit boundary.Disengagement of haptic control might occur for various reasons, one ofwhich relates to a temporary inability of the navigation system 10 todetect the pose of one or more tracked objects. For example, somenavigation systems require a clear path between a detection device 12and the trackable elements, such as navigation markers 14 and 16, hapticdevice marker 18, and end effector marker 19 (FIG. 1). If one of thetrackable elements is temporarily blocked (i.e. occluded), thenavigation system 10 may not be able to effectively determine the poseof one or more tracked objects. As a safety precaution, when a trackableelement becomes occluded during a surgical procedure, the surgicalsystem 100 may disengage haptic control of the surgical tool 36. Hapticcontrol may also be disengaged due to sudden movement of a trackedobject. For example, the patient's leg or the robotic arm 34 may bebumped, and the navigation system 10 is unable to accurately track thesuddenly-moved object. The surgical system will therefore disengagehaptic control of the surgical tool 36. Disengagement of haptic controlcauses the haptic device 30 to enter free mode. The haptic restorationfeature can then be utilized to either reengage haptic control byreactivating haptic object 52 or to retain the haptic device 30 in freemode and require the surgeon to reenter entry boundary 50.

To determine whether to reengage haptic control or whether to retain thehaptic device 30 in free mode, the surgical system 100 is programmed toevaluate whether various conditions are met after the occlusion, suddenmovement, or other factor has caused disengagement of haptic control. Ingeneral, the conditions may relate to the position or orientation of asurgical tool 36 relative to the desired, constrained position ororientation of surgical tool 36, and the conditions may depend on thetype of surgical tool 36 and the configuration of haptic object 52.Three possible conditions to evaluate may be the tool's orientation,vertical penetration in a haptic plane, and whether all HIPs are withinthe haptic boundaries. For example, the embodiment of FIG. 15 includes avirtual blade 82, which represents a sagittal saw and includes multipleHIPs (as indicated above, although only one HIP 60 is labeled,references to HIP 60 include references to multiple HIPs). FIG. 15 alsoincludes a planar haptic object 52. In this embodiment, the hapticrestoration feature may include determining the orientation of virtualblade 82 relative to haptic object 52 by calculating the angle betweentool normal 48 and haptic object normal 62. Tool normal 48 and hapticobject normal 62 are ideally parallel if the surgical tool 36 is beingconstrained during cutting to lie within the working boundarycorresponding to planar haptic object 52. One condition may be, forexample, whether tool normal 48 and haptic object normal 62 are withintwo degrees of each other. The surgical system 100 can be programmed toconclude that if this condition is met, the orientation of surgical tool36 remains substantially accurate even after the temporary occlusion ofa trackable element or sudden movement of the patient or robotic arm.The surgical system 100 may also evaluate the position of HIP 60relative to planar haptic object 52 (e.g., vertical penetration). FIG.15 illustrates virtual boundaries 102, 104 above and below haptic object52. Virtual boundaries 102, 104, can be planned to lie, for example,approximately 0.5 mm away from haptic object 52. A second condition maybe whether HIP 60 lies between these virtual boundaries 102, 104. Asanother example, a third condition may be whether each of the HIPs 60 ofvirtual blade 82 lie within the outer bounds of haptic object 52.

If each of the relevant conditions are met, the haptic restorationfeature reactivates haptic object 52, which reengages haptic control andallows the surgeon to continue cutting. However, if any of theconditions are not met, the haptic device 30 remains in free mode. Thesurgeon must then cause HIP 60 to cross back into an entry boundary 50(not shown in FIG. 15), as described in the various embodiments herein.Once HIP 60 crosses entry boundary 50, haptic control can be reengaged.In the embodiment illustrated in FIG. 15, haptic control after HIP 60has crossed entry boundary 50 may include automatic alignment andsubsequent constraint of HIP 60 on planar haptic object 52. In otherembodiments, such as the embodiment of FIGS. 13A-13D, haptic controlafter HIP 60 crosses entry boundary 50 may not include automaticalignment.

The construction and arrangement of the systems and methods as shown inthe various exemplary embodiments are illustrative only. Although only afew embodiments have been described in detail in this disclosure, manymodifications are possible (e.g., variations in sizes, dimensions,structures, shapes and proportions of the various elements, values ofparameters, use of materials, colors, orientations, etc.). For example,the position of elements may be reversed or otherwise varied and thenature or number of discrete elements or positions may be altered orvaried. Accordingly, all such modifications are intended to be includedwithin the scope of the present disclosure. The order or sequence of anyprocess or method steps may be varied or re-sequenced according toalternative embodiments. Other substitutions, modifications, changes,and omissions may be made in the design, operating conditions andarrangement of the exemplary embodiments without departing from thescope of the present disclosure.

The present disclosure contemplates methods, systems and programproducts on any machine-readable media for accomplishing variousoperations. The embodiments of the present disclosure may be implementedusing existing computer processors, or by a special purpose computerprocessor for an appropriate system, incorporated for this or anotherpurpose, or by a hardwired system. Embodiments within the scope of thepresent disclosure include program products comprising machine-readablemedia for carrying or having machine-executable instructions or datastructures stored thereon. Such machine-readable media can be anyavailable media that can be accessed by a general purpose or specialpurpose computer or other machine with a processor. By way of example,such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROMor other optical disk storage, magnetic disk storage, other magneticstorage devices, solid state storage devices, or any other medium whichcan be used to carry or store desired program code in the form ofmachine-executable instructions or data structures and which can beaccessed by a general purpose or special purpose computer or othermachine with a processor. When information is transferred or providedover a network or another communications connection (either hardwired,wireless, or a combination of hardwired or wireless) to a machine, themachine properly views the connection as a machine-readable medium.Thus, any such connection is properly termed a machine-readable medium.Combinations of the above are also included within the scope ofmachine-readable media. Machine-executable instructions include, forexample, instructions and data which cause a general purpose computer,special purpose computer, or special purpose processing machines toperform a certain function or group of functions.

Although a specific order of method steps may be described, the order ofthe steps may differ from what is described. Also, two or more steps maybe performed concurrently or with partial concurrence (e.g. deactivationof entry boundary 50 and activation of exit boundary 64). Such variationwill depend on the software and hardware systems chosen and on designerchoice. All such variations are within the scope of the disclosure.Likewise, software implementations could be accomplished with standardprogramming techniques with rule based logic and other logic toaccomplish any connection steps, processing steps, comparison steps, anddecision steps.

What is claimed is:
 1. A surgical system, comprising: a haptic device; asurgical tool coupled to the haptic device and associated with a virtualhaptic interaction point, wherein movement of the virtual hapticinteraction point corresponds to movement of the surgical tool; and aprocessing circuit comprising a computer-readable storage medium havinginstructions stored thereon, that when executed by the processingcircuit cause the processing circuit to: establish a virtual entryboundary, wherein the virtual entry boundary is configured such that aninteraction between the virtual haptic interaction point and the virtualentry boundary triggers the haptic device to switch from a free mode toan automatic alignment mode, wherein in the free mode the surgical toolis capable of being manually manipulated by a user, and in the automaticalignment mode the surgical tool is capable of being automaticallyaligned with a haptic object by the haptic device; detect an alignmentaction being performed by a user; initiate automatic alignment of thesurgical tool with the haptic object in the automatic alignment mode inresponse to detecting the alignment action being performed by the user;and constrain the surgical tool in a haptic control mode of the hapticdevice after the surgical tool is aligned with the haptic object.
 2. Thesurgical system of claim 1, wherein the processing circuit is furtherconfigured to continue automatic alignment of the surgical tool with thehaptic object in the automatic alignment mode so long as detection ofthe alignment action continues.
 3. The surgical system of claim 1,further comprising a trigger associated with the surgical tool, whereinthe alignment action includes depressing the trigger.
 4. The surgicalsystem of claim 1, further comprising a sensor associated with thesurgical tool, wherein the alignment action includes placing a hand ofthe user so as to be sensed by the sensor.
 5. The surgical system ofclaim 1, wherein the surgical tool includes a sagittal saw.
 6. Thesurgical system of claim 5, wherein the processing circuit is furtherconfigured to automatically move the sagittal saw into alignment with aplane of the haptic object in the automatic alignment mode.
 7. Thesurgical system of claim 6, wherein the processing circuit is furtherconfigured to constrain the sagittal saw in the haptic control mode tokeep the sagittal saw in alignment with the plane of the haptic object.8. The surgical system of claim 7, wherein the sagittal saw isassociated with a plurality of virtual haptic interaction points and theprocessing circuit is further configured to automatically modify atleast one of an orientation and a position of the sagittal saw based onpositions of the plurality of virtual haptic interaction points.
 9. Thesurgical system of claim 1, wherein the virtual entry boundary enclosesa three-dimensional volume.
 10. A method of using a surgical systemcomprising a haptic device, a surgical tool coupled to the haptic deviceand associated with a virtual haptic interaction point, and a processingcircuit comprising a computer-readable storage medium havinginstructions stored thereon, said method comprising the steps of:establishing a virtual entry boundary, wherein the virtual entryboundary is configured such that an interaction between the virtualhaptic interaction point and the virtual entry boundary triggers thehaptic device to switch from a free mode to an automatic alignment mode,wherein in the free mode the surgical tool is capable of being manuallymanipulated by a user, and in the automatic alignment mode the surgicaltool is capable of being automatically aligned with a haptic object bythe haptic device; detecting an alignment action being performed by theuser; initiating automatic alignment of the surgical tool with thehaptic object in the automatic alignment mode in response to detectingthe alignment action being performed by the user; and constraining thesurgical tool in a haptic control mode of the haptic device after thesurgical tool is aligned with the haptic object.
 11. The method of claim10, further comprising continuing automatic alignment of the surgicaltool with the haptic object in the automatic alignment mode so long asdetection of the alignment action continues.
 12. The method of claim 10,wherein detecting the alignment action includes detecting the userdepressing a trigger.
 13. The method of claim 10, wherein detecting thealignment action includes sensing the user.
 14. The method of claim 10,wherein the surgical tool includes a sagittal saw.
 15. The method ofclaim 14, further comprising automatically moving the sagittal saw intoalignment with a plane of the haptic object in the automatic alignmentmode.
 16. The method of claim 15, further comprising constraining thesagittal saw in the haptic control mode to keep the sagittal saw inalignment with the plane of the haptic object.
 17. The method of claim16, wherein the sagittal saw is associated with a plurality of virtualhaptic interaction points.
 18. The method of claim 17, furthercomprising automatically modifying at least one of an orientation and aposition of the sagittal saw based on positions of the plurality ofvirtual haptic interaction points.
 19. The method of claim 10, whereinthe virtual entry boundary encloses a three-dimensional volume.
 20. Acomputer-readable storage medium having instructions thereon that, whenexecuted by a processing circuit, aid in the planning or performance ofa surgical procedure, the medium comprising: instructions forassociating a virtual haptic interaction point with a surgical toolcoupled to a haptic device; instructions for establishing a virtualentry boundary, wherein the virtual entry boundary is configured suchthat an interaction between the virtual haptic interaction point and thevirtual entry boundary triggers the haptic device to switch from a freemode to an automatic alignment mode, wherein in the free mode thesurgical tool is capable of being manually manipulated by a user, and inthe automatic alignment mode the surgical tool is capable of beingautomatically aligned with a haptic object; instructions for detectingan alignment action being performed by the user; instructions forinitiating automatic alignment of the surgical tool with the hapticobject in the automatic alignment mode in response to detecting thealignment action being performed by the user; and instructions forconstraining the surgical tool in a haptic control mode of the hapticdevice after the surgical tool is aligned with the haptic object.